User:1sfoerster/Power Supply

Problem Statement

 * Testing a DC power supply by measuring voltage doesn't necessarily mean that it will supply enough current. A method of varying the load and measuring the current is needed to test DC constant voltage supplies.

Design

 * A circuit was designed and simulated at circuitlab.


 * It then was modified to fit the parts on hand:


 * Final Circuit

Theory of Operation

 * video

Materials

 * 2N3055 Power transistor $1.55 * 4 = $6
 * 5K ohm pot $3 * 2 = $6
 * .3 ohm 100 watt resistors 8*$5.17 = $42
 * 35 &Omega; low power potentiometer
 * 2.4 K&Omega; low power resistor
 * 5 K&Omega; low power resistor
 * 2 K&Omega; low power potentiometer
 * 2 K&Omega; low power resistor
 * 100 ohm resistor
 * Case
 * meter movement to turn into a meter
 * knobs, 12 gauge wire, 24 gauge wire
 * 2 heat sinks (from broken PC power supplies)
 * board (piece of wood)
 * bread board

Assembly
Steps:
 * 1) Take a heat sinks and a transistor, mark where to drill the mount holes and post holes for the transistors are to be mounted.
 * 2) Do the same for the other heat sink.
 * 3) Drill the holes for the posts with the 3/8" bit and the holes for mounting transistors with the 3/32" bit.
 * 4) Tap mount holes with 1/8" tap.
 * 5) Take all four power resistors and evenly space them apart at one end of the board.
 * 6) Use the wood screws to attach to the board.
 * 7) Peal the plastic from the tape on the bottom of the bread board and attach it to the wood a couple of inches above the resistors.
 * 8) Take one of the heat sinks and mount the transistors to it. Use two of the 1 1/2" screws at at the end of the heat sink and the 1/2" screws for the middle mount holes. The 1 1/2" screws will be used for mounting the heat sinks later.
 * 9) Repeat step 8 for the other heat sink.
 * 10) Take one of the heat sinks and turn it over. Using the 12 gauge wire, solder the wire to the base and emitter as seen in picture. Be sure to clamp the heat sink to the post before you solder, to help protect the transistor from being damaged.
 * 11) Turn the heat sink back over and line up the towards the end of the board with the longer screws 1" in from the side of the board. Using the rubber mallet, tap the screws to make a mark on the board. This is where you will drill the hole to mount the heat sinks.
 * 12) Now drill the mount holes the you just marked, using the 3/32" bit.
 * 13) Back the 1 1/2" screws out half way.line the screws up with the holes, now screw the into the holes.

Meter Movement
Reference document: Conversion of voltmeter to ammeter

First Meter Movement
Destroyed meter movement and burned up resistor by hooking directly to power supply. Meter movements take very little energy to swing full scale.

Conclusion: a much larger internal resistor is needed.

Second Meter Movement
Using meter movement out of old photometer.

Has an internal resistance of 900 ohms.

Tutorials

 * mosfets
 * potentiometers/knobs
 * power resistors
 * heat sink

Next Steps

 * Need revised circuit made public and linked up
 * Need simulation of revised circuit compared with original circuit
 * Work is needed on the theory of operation
 * Need to start an operations manual
 * Need power section wiring replaced with 12 gauge, thick wire
 * Get approval of instructor before testing second meter movement